From: Darrick J. Wong <darrick.wong@xxxxxxxxxx> An internal customer followed an erroneous AskUbuntu article[1] to try to change the UUID of a live ext4 filesystem. The article claims that you can work around tune2fs' "cannot change UUID on live fs" error by disabling uninit_bg, changing the UUID, and re-enabling the feature. This led to metadata corruption because tune2fs' journal descriptor rewrite races with regular filesystem writes. Therefore, prevent administrators from turning on or off uninit_bg on a mounted fs. [1] https://askubuntu.com/questions/132079/how-do-i-change-uuid-of-a-disk-to-whatever-i-want/195839#459097 Signed-off-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx> --- misc/tune2fs.c | 12 ++++++++++++ 1 file changed, 12 insertions(+) diff --git a/misc/tune2fs.c b/misc/tune2fs.c index 8368a733..150dc916 100644 --- a/misc/tune2fs.c +++ b/misc/tune2fs.c @@ -1312,6 +1312,12 @@ static int update_feature_set(ext2_filsys fs, char *features) if (FEATURE_ON(E2P_FEATURE_RO_INCOMPAT, EXT4_FEATURE_RO_COMPAT_GDT_CSUM)) { + if (mount_flags & EXT2_MF_MOUNTED) { + fputs(_("Cannot enable uninit_bg on a mounted " + "filesystem!\n"), stderr); + exit(1); + } + /* Do not enable uninit_bg when metadata_csum enabled */ if (ext2fs_has_feature_metadata_csum(fs->super)) ext2fs_clear_feature_gdt_csum(fs->super); @@ -1321,6 +1327,12 @@ static int update_feature_set(ext2_filsys fs, char *features) if (FEATURE_OFF(E2P_FEATURE_RO_INCOMPAT, EXT4_FEATURE_RO_COMPAT_GDT_CSUM)) { + if (mount_flags & EXT2_MF_MOUNTED) { + fputs(_("Cannot disable uninit_bg on a mounted " + "filesystem!\n"), stderr); + exit(1); + } + err = disable_uninit_bg(fs, EXT4_FEATURE_RO_COMPAT_GDT_CSUM); if (err)
